1. Field of the Invention
The present invention relates to a lithium ion secondary battery and a method of manufacturing the same, the lithium ion secondary battery including: a positive electrode sheet that includes a positive electrode active material layer containing positive electrode active material particles; a negative electrode sheet; and a nonaqueous electrolytic solution that contains a compound containing fluorine.
2. Description of Related Art
It is known that, in a lithium ion secondary battery (hereinafter, referred to simply as “battery”), the voltage is high during charging; therefore, a nonaqueous solvent of a nonaqueous electrolytic solution is likely to be oxidized and decomposed on particle surfaces of positive electrode active material particles. When the nonaqueous electrolytic solution contains a compound containing fluorine, hydrogen ions, which are produced by the oxidation decomposition of the nonaqueous solvent, may react with fluorine to produce hydrofluoric acid (HF). As a result, due to the action of the hydrofluoric acid, transition metal is eluted from the positive electrode active material particles, and the battery capacity decreases. Therefore, this battery has a problem in that the battery capacity significantly decreases in a charging-discharging cycle test.
As a countermeasure against the problem, a technique of forming a film containing fluorine on particle surfaces of positive electrode active material particles is known. By covering the particle surfaces of the positive electrode active material particles with the film, direct contact between the nonaqueous electrolytic solution and the positive electrode active material can be suppressed. Therefore, the oxidation decomposition of the nonaqueous solvent of the nonaqueous electrolytic solution during charging or the like can be suppressed. In particular, fluorine is not likely to be oxidized, and the film containing fluorine is strong. Therefore, the oxidation decomposition of the nonaqueous solvent can be efficiently suppressed. Accordingly, when the charging-discharging cycle test is performed on the battery, a decrease in battery capacity can be suppressed. For example, Japanese Patent Application Publication No. 2012-181975 (JP 2012-181975 A) discloses a battery including a film containing fluorine that is formed on particle surfaces of positive electrode active material particles of a lithium nickel manganese composite oxide which contains at least nickel and manganese as transition metal (refer to claims in JP 2012-181975 A).
However, since the film containing fluorine is a resistor, the battery resistance is likely to increase due to the film.